Over the past twenty years, computer technology has evolved very rapidly. One aspect of this evolution has been a progressively growing demand for increased storage capacity in memory devices, especially where the information storage medium is some form of removable component. In this regard, just a little over a decade ago, the typical personal computer had a floppy disk drive which accepted floppy disk cartridges that contained a 5.25″ disk with a storage capacity up to about 720 kilobytes (KB) per cartridge. Not long thereafter, these devices gave way to a new generation of floppy disk drives which accepted smaller floppy disk cartridges that contained a 3.5″ disk with higher storage capacities, up to about 1.44 MB per cartridge.
Subsequently, as the evolution continued, a further significant increase in storage capacity was realized in the industry by the introduction of the removable optical disk. One such optical disk is commonly known as a compact disk (CD). Even more recently, a further type of optical disk was introduced, and is commonly known as a Digital Versatile Disk (DVD).
The compact disk has an information storage surface with a plurality of tracks that each have therealong a series of optical data pits of variable length. This variable pit length recording is termed run-length-limited (RLL) encoding. By using RLL, present optical data storage products (CD and DVD) are able to encode information onto an optical media with pit lengths shorter than the spot size of a laser stylus used for recording and reading data in these products. In order is used. This rule set for present optical products (CD and DVD) converts data bits into recorded channel bits with a 1:2 efficiency. That is, two optical media recorded channel bits are used to encode one data bit. This is thus part of the factors that define what size media area under present optical data storage standards can be considered to be a single bit optical data element. An optical data element hence is the area required for storage of one basic unit of information on the data storage media. For CD and DVD technologies, this basic unit is one bit (“1” or “0”) of data. For example, with the requirements of RLL overhead factored in, the size of a CD optical data element storing one bit of user data has a size of about 1.6 microns by 0.56 microns.
The DVD disk has either one or two layers of information storage surfaces, only one of which is read or written at any given point in time. Each information storage surface includes a plurality of tracks that, like a compact disk, each have therealong a series of optical data elements reduced in size and configuration from that of the optical data elements of a compact disk. In particular, for each optical data element, which represents a user single binary bit which is a binary “0” or “1”, the user optical data element size is reduced to about 0.74 microns by 0.26 microns. The similarity between the formats from the optical data element size perspective is that the approximate ratio in the dimensions is 3:1. The larger of the two dimensions is the data track pitch in both the CD and DVD case.
Although these pre-existing optical disks have been generally adequate for their intended purposes, there is still a progressively growing demand for increased storage capacity in optical storage media. In addition, there is also a need for an increase in the rate at which information can be read from optical media. Also, to the extent that some form of higher capacity optical media is provided, it is desirable that it have a cost per unit which is in approximately the same range as the cost of existing compact disks or DVD disks. Further, to the extent that some such higher capacity optical media is provided, it is desirable that a detection system capable of reading it be compatible with pre-existing compact disks and/or DVD disks, while having a cost which is not significantly greater than that of existing detection systems used for existing disks.